Applicants claim, under 35 U.S.C. xc2xa7 119, the benefit of priority of the filing date of Jan. 10, 2002 of a German patent application, copy attached, Ser. No. 102 00 587.7, filed on the aforementioned date, the entire contents of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to a method for the incremental position determination of two objects which are movable in relation to each other. The present invention moreover relates to a device for executing the method.
2. Discussion of Related Art
Incremental position measuring systems for determining the position of objects which can be moved in relation to each other are known, which detect relative movements of the objects in relation to each other in defined measurement steps, or increments. The incremental position measuring systems used for this purpose have, for example, a scale with an incremental measuring graduation, which is connected with one of the two objects, as well as a scanning unit, which is connected with the other of the two objects. Customarily a pair of position-dependent incremental scanning signals, which have a defined phase offset with respect to each other, is generated by optical, magnetic, inductive or capacitive scanning. Alternatively to the above described position measuring systems with physically embodied scale graduations it is however also possible to generate such scanning signals with the aid of a laser interferometer. In this case the respective airwave length is used as the measuring standard.
In many application cases the most diverse transformation operations with respect to the generated scanning signals are required prior to the actual further processing of the scanning signals in a downstream-connected evaluation unit, for example a numerical machine tool control device.
The interpolation of the scanning signals can for example be performed as a transformation operation for increasing the resolution of such position measuring systems. This should be understood to be a further electronic division, or multiplication, of the delivered signal periods of the scanning signals. Expressed mathematically, in this case the interpolation is a coordinate transformation from Cartesian coordinates into polar coordinates.
A correction of the scanning signals with respect to possibly present amplitude and/or offset errors can be provided within the scope of a further transformation operation prior to actual further processing.
A method and a device for processing incremental scanning signals is proposed in the publication DE 44 43 898 C2, wherein various transformation operations are performed prior to further processing. Thus, besides an interpolation of the scanning signals, a further correction of the scanning signals is performed in accordance with the publication. A first transformation table in the form of an interpolation table to which the digital scanning signals are provided in pairs is used for interpolation. The digitized scanning signals are used for addressing the first transformation table, in which an output signal value in the form of a defined interpolation value is assigned to each pair of input signal values present. An interpolation value which corresponds to a fraction of a signal period of the scanning signals is applied to the output of the first transformation table. A second transformation table follows the first transformation table and is used for the correction of errors in the period start and period length. Additional errors in the scanning signals, such as amplitude errors and offset errors, are corrected in a third transformation table, which is placed ahead of the first transformation table.
In connection with the above described device, or the above described method it should be noted that neither the device nor the method provides the possibility of providing flexible correction of errors in the scanning signals, which change or vary in the course of the actual position measurement. If, for example, a transformation table were to be provided for this, in which the correct output signal values of all conceivable input signal values would be stored, a very large transformation table with a correspondingly large need for memory would be required for this.
It is therefore an object of the present invention to disclose a method and a device for incremental position determination, by which a flexible transformation of the generated scanning signals is assured without a large outlay for computing and memory.
This object is attained by a method for the incremental position determination of two objects, which are movable in relation to each other. The method including generating at least one pair of position-dependent incremental scanning signals during a position determination between two objects, which have a defined phase offset from each other. Passing the at least one pair of position-dependent incremental scanning signals on to a transformation table in which one or several output signal values with respect to each pair of the at least one pair of position-dependent incremental scanning signals have been stored. Transferring the one or several output signals from the transformation table to an evaluation unit wherein position determination between the two objects is performed. Dynamically updating the transformation table during the position determination between the two objects.
The stated object is furthermore attained by a device for the incremental position determination of two objects, which are movable in relation to each other. The device includes a position signal generator that generates at least one pair of position-dependent incremental scanning signals, which have a defined phase offset from each other and represent a position between two objects. A transformation table to which at least one of the at least one pair of position-dependent incremental scanning signals is passed, wherein one or several output signal values with respect to each of the at least one pair of position-dependent incremental scanning signals are stored in the transformation table, wherein the transformation table is dynamically updated in the course of determining the position between the two objects. An evaluation unit that receives the one or several output signals and determines the position between the two objects based on said one or several output signal values.
In accordance with the present invention it is now provided to embody the transformation table used for transforming the scanning signals so that it can dynamically updated. In this way a small processing outlay during the actual transformation, as well as a small outlay for memory for the transformation table, are required.
Depending on the embodiment of the transformation table which can be dynamically updated, a first transformation table, or at least a first portion of a transformation table, is used for the actual transformation operation, while at the same time a second transformation table, or a second portion of a transformation table, is being updated in the background.
The most varied transformation operations are considered within the scope of the present invention. Typical transformation operations are, for example, a signal interpolation and/or a signal correction taking place, etc. As mentioned above, the signal interpolation is understood to be a coordinate transformation from Cartesian coordinates to polar coordinates.
In principle, several such transformation tables can be used in cascaded arrangements, wherein each one of the individual transformation tables takes on a defined transformation operation. However, alternatively to this it is also possible to provide only a single transformation table, in which different transformation operations are simultaneously performed, for example the simultaneous signal interpolation and signal correction, etc.
The measures in accordance with the present invention can be employed in connection with incremental position measuring systems with physically embodied scale graduations, as well as with laser interferometers.
Furthermore, linear position measuring systems, as well as rotatory position measuring systems, can be embodied in accordance with the present invention.
Further advantages, as well as details of the present invention ensue from the subsequent description of exemplary embodiments, making reference to the attached drawings.